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Blends of poly(ester amide) polymersRelated Patent Categories: Synthetic Resins Or Natural Rubbers -- Part Of The Class 520 Series, Natural Rubber Compositions Having Nonreactive Materials (dnrm) Other Than: Carbon, Silicon Dioxide, Glass Titanium Dioxide, Water, Hydrocarbon, Halohydrocarbon, Ethylenically Unsaturated Reactant Admixed With A Preformed Reaction Product Derived From: (a) At Least One Polycarboxylic Acid, Ester, Or Anhydride; (b) At Least One Polyhydroxy Compound; And (c) At Least One Fatty Acid Glycerol Ester, Or A Fatty Acid Or Salt Derived From A Naturally Occurring Glyceride, Tall Oil, Or A Tall Oil Fatty Acid, Solid Polymer Derived From At Least One Carboxylic Acid Or Derivative, Solid Polymer Derived From At Least One Lactam; From An Amino Carboxylic Acid Or Derivative; Or From A Polycarboxylic Acid Or Derivative, Solid Polymer Derived From An Amino Carboxylic Acid Or Derivative; From A Polyamine And A Polycarboxylic Acid Or Derivative; From At Least One Lactam; Or From A Polyamine Salt Of A Polycarboxylic Acid, Mixed With Polycarboxylic Acid Or Derivative And Polyhydroxy Reactant Or Polymer TherefromBlends of poly(ester amide) polymers description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20070093617, Blends of poly(ester amide) polymers. Brief Patent Description - Full Patent Description - Patent Application Claims
CROSS REFERENCE TO RELATED APPLICATION [0001] This is a continuation application of U.S. application Ser. No. 10/960,381, filed on Oct. 6, 2004, the teaching of which is incorporated herein in its entirety. BACKGROUND OF THE INVENTION [0002] 1. Field of the Invention [0003] This invention generally relates to blends of poly(ester amide) (PEA) polymers or copolymers with a low glass transition temperature (T.sub.g) and PEA polymers or copolymers with a high T.sub.g, which are useful for coating an implantable device such as a drug-delivery stent. [0004] 2. Description of the Background [0005] Poly(ester amide) polymers are known for their relatively low glass transition temperatures. For example, co-poly-{[N,N'-sebacoyl-bis-(L-leucine)-1,6-hexylene diester]-[N,N'-sebacoyl-L-lysine benzyl ester]} (PEA-Bz) and co-poly{[N,N'-sebacoyl-bis-(L-leucine)-1,6-hexylene, diester]-[N,N'-sebacoyl-L-lysine 2,2,6,6-tetramethyl-4-amino-1-piperidinyloxyl amide]} (PEA-TEMPO) have a T.sub.g of approximately 23.degree. C. and 33.degree. C., respectively. [0006] Complications related to low T.sub.g manifest themselves as reduced drug release rate control, increased polymer degradation rate, reduced shelf life stability, and potentially increased system mechanical failures. Low T.sub.g materials usually have higher drug permeabilities, which necessitates the use of greater amounts of polymer to control release rate of the drug. Moreover, the low T.sub.g enables the drug to diffuse within the coating. In other words, the drug distribution within a given coating can change with time until an equilibrium state is reached, resulting in release rate shifts. Low T.sub.g materials also tend to be softer, they can be more adhesive to balloons, and are more prone to failure during mechanical perturbations such as crimping and expansion. [0007] The embodiments of the present invention provide for methods addressing these issues. SUMMARY OF THE INVENTION [0008] Provided herein are polymer blends that include poly(ester amide) (PEA) polymers or copolymers with a low T.sub.g and PEA polymers or copolymers with a high T.sub.g. The polymer blends provided herein can form coatings that have improved stability, drug release rate, and mechanical characteristics. The polymer blends can be fine-tuned to have different polymer degradation rates in that, as the effective T.sub.g of the polymer blend is increased, the degradation rate of the polymer blend will decrease. [0009] The PEA polymer blend has an effective T.sub.g equal to or above the T.sub.g of PEA-Bz. In some embodiments, the PEA polymer blend has an effective T.sub.g of about 23.degree. C. or above. The PEA polymer blends described herein can be used to coat an implantable device or to form the implantable device itself, one example of which is a stent. In some embodiments, the PEA polymer blends can be used optionally with a biobeneficial material and/or optionally a bioactive agent to coat an implantable device. In some other embodiments, the PEA polymer blends can be used with one or more biocompatible polymers, which can be biodegradable, bioabsorbable, non-degradable, or non-bioabsorbable polymer. [0010] The implantable device can be a stent that can be a metallic, biodegradable or nondegradable stent. The stent can be intended for neurovasculature, carotid, coronary, puhnonary, aorta, renal, biliary, iliac, femoral, popliteal, or other peripheral vasculature. The stent can be used to treat or prevent a disorder such as atherosclerosis, thrombosis, restenosis, hemorrhage, vascular dissection or perforation, vascular aneurysm, vulnerable plaque, chronic total occlusion, claudication, anastomotic proliferation for vein and artificial grafts, bile duct obstruction, ureter obstruction, tumor obstruction, or combinations thereof. DETAILED DESCRIPTION [0011] Provided herein are polymer blends that include poly(ester amide) (PEA) polymers or copolymers with a low T.sub.g and PEA polymers or copolymers with a high T.sub.g. The polymer blends provided herein can form coatings that have improved stability, drug release rate, and mechanical characteristics. The polymer blends can be fine-tuned to have different polymer degradation rates in that, as the effective T.sub.g of the polymer blend is increased, the degradation rate of the polymer blend will decrease. [0012] T.sub.g as used herein generally refers to the temperature at which the amorphous domains of a polymer change from a brittle vitreous state to a plastic state at atmospheric pressure. In other words, T.sub.g corresponds to the temperature where the onset of segmental motion in the chains of the polymer occurs, and it is discernible in a heat-capacity-versus-temperature graph for a polymer. When an amorphous or semicrystalline polymer is heated, its coefficient of expansion and heat capacity both increase as the temperature rises, indicating increased molecular motion. As the temperature rises, the polymer's actual molecular volume remains constant. Therefore, a higher coefficient of expansion points to a free volume increase of the system and increased freedom of movement for the molecules. The term "low T.sub.g" refers to a T.sub.g of a low T.sub.g material (generally below about 30.degree. C.), e.g., the T.sub.g of PEA-Bz, which has a structure of --[-sebacinate-L-Leu-hexanediol-L-Leu-].sub.m-[-sebacinate-Lys benzyl ester-].sub.n-- Formula 1 where m and n are independent positive integers ranging from, e.g., 1 to 100,000. [0013] The PEA polymers forming the blend are substantially mutually soluble in that. one polymer has a solubility of at least about 1 wt %, at least about 5 wt %, at least about 10 wt %, at least about 20 wt %, at least about 50 wt %, at least about 75 wt %, at least about 90 wt %, or at least about 99 wt % in the other polymer and vice versa. In some embodiments, the PEA polymers forming the blend can be substantially thermodynamically miscible, for example, the PEA polymers forming the polymer blend will not phase-separate into microdomains. In some other embodiments, the PEA polymers forming the blend may be mechanically compatible. Mechanically compatible blends are composite systems where the mechanical properties of the blend are not degraded or improved when compared to the individual components that make up the blend as a result of relatively uniform and consistent microphase separation. In contrast, mechanically incompatible blends have degraded mechanical properties when compared to the properties of the individual components as a result of exhibiting gross phase separation. Mechanically incompatible blends typically exhibit low elongation and brittle failure. [0014] The PEA polymer blend has an effective T.sub.g equal to or above the T.sub.g of PEA-Bz. As used herein, the term "effective T.sub.g" refers to the T.sub.g of a blend of materials having different T.sub.gs. In some embodiments, the PEA polymer blend has an effective T.sub.g of about 23.degree. C. or above. However, raising the effective T.sub.g too high will result in a loss of mechanical integrity, and potentially too low a drug release rate. A preferred range of the effective T.sub.g of the PEA polymer blend is in the range, for example, between about 23.degree. C. and about 75.degree. C. The effective T.sub.g of a thermodynamically compatible polymer blend can be calculated according to the formula 1/T.sub.g mix=W.sub.1/T.sub.g1+W.sub.2/T.sub.g2, where T.sub.g mix is the glass transition of the blend, while W.sub.1, W.sub.2, T.sub.g1 and T.sub.g2 are the weight fractions and glass transition temperatures of each of the components. For more than 2 components, this equation can be generalized as: 1/T.sub.g mix=.SIGMA.W.sub.i/T.sub.gi where .SIGMA. represents the summation of i components. Alternatively, the formula is often represented as follows: T.sub.g mix=.phi..sub.1T.sub.g1+.phi..sub.2T.sub.g2, where .phi. represents the volume fraction of each component. [0015] The PEA polymer blends described herein can be used to coat an implantable device or to form the implantable device itself, one example of which is a stent. In some embodiments, the PEA polymer blends can be used optionally with a biobeneficial material and/or optionally a bioactive agent to coat an implantable device. In some other embodiments, the PEA polymer blends can be used with one or more biocompatible polymers, which can be biodegradable, bioabsorbable, non-degradable, or non-bioabsorbable polymers. [0016] The implantable device can be a stent that can be metallic, biodegradable or nondegradable. The stent can be intended for neurovasculature, carotid, coronary, pulmonary, aortic, renal, biliary, iliac, femoral, popliteal, or other peripheral vasculature. The stent can be used to treat or prevent a disorder such as atherosclerosis, thrombosis, restenosis, hemorrhage, vascular dissection or perforation, vascular aneurysm, vulnerable plaque, chronic total occlusion, claudication, anastomotic proliferation for vein and artificial grafts, bile duct obstruction, ureter obstruction, tumor obstruction, or combinations thereof. Modification of Poly(Ester Amide) (PEA) Polymers [0017] In some embodiments, PEA polymers with a high T.sub.g can be formed by modifying a PEA polymer having at least one ester grouping and at least one amide grouping in the backbone that has a low T.sub.g. In one embodiment, the low T.sub.g polymer can be a PEA having three building blocks: an amino acid, a diol, and a diacid. The diacid is preferably a C2-C12 diacid, aliphatic or with unsaturation. The amino acid can be, for example, glycine, valine, alanine, proline, glutamine, methionine, leucine, isoleucine, or phenylalanine. An optional second amino acid may be included. The second amino acid can be, for example, lysine, tyrosine, tryptophan, arginine, histidine, glutamic acid, aspartic acid, threonine, serine, or cysteine. The second amino acid may contain a side group to enable the attachment of pharmacologically active compounds or property modifiers. PEA polymers with various thermal properties can be readily prepared by varying these components during synthesis. [0018] Generally, decreasing the polymethylene chain length of the diol or diacid building block will increase the T.sub.g. PEA polymers based on amino acids with optical rotation (e.g., L-isomers) will have higher T.sub.g than those based on the corresponding racemic amino acids (D,L-isomers). PEA polymers synthesized from optically active L-amino acids with symmetrical side substituents (e.g., valine, leucine, phenylalanine) will have higher T.sub.gs than those synthesized from L-amino acids with nonsymmetrical side substituents (e.g., isoleucine). Amino acids with aromatic substituents (e.g., phenylalanine) tend to have higher T.sub.gs. [0019] In one embodiment, the PEA polymer with a low T.sub.g can be PEA-Bz. PEA-Bz can be modified to replace a side group or a backbone group thereof to increase the T.sub.g of the polymer. Some strategies of modifying PEA-Bz to increase T.sub.g are described below. Continue reading about Blends of poly(ester amide) polymers... Full patent description for Blends of poly(ester amide) polymers Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Blends of poly(ester amide) polymers patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. 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